In the fabrication processes for semiconductor devices, a semi-conducting wafer is normally processed through many different fabrication steps, i.e., sometimes as many as several hundred. These processing steps may include deposition processes, etching processes, ion implantation processes and a variety of other processes. The fabrication equipment utilized in these processes may include process chambers that are arranged in a cluster formation with a center loadlock chamber for delivering and withdrawing wafers to and from each process chamber.
One of the key components in a loadlock chamber is a wafer blade that is normally controlled by a robotic arm. The wafer blade is also known as a robot blade. The robot blade can be constructed of a thin piece of metal such that it holds a wafer securely for delivering it into process chambers through narrow slit valves provided in the sides of the process chambers that join the loadlock chamber.
In a typical loadlock chamber, a robot blade and a storage elevator are provided. The loadlock chamber provides a wafer handling center in a clustered processing machine by isolating the plurality of process chambers from the surrounding atmosphere through the use of slit valves between the loadlock chamber and the process chambers. A cassette indexer or a SMIF pod may provide the source of wafers for the robot blade in the loadlock chamber. The loadlock chamber is normally provided with a self-contained vacuum system that maintains the interior of the chamber particle free and at a slightly higher pressure than the process chambers during wafer transfers to and from the process chambers. The self-contained vacuum system further provides the loadlock chamber with atmospheric pressure during wafer transfers to and from a cassette indexer. In a normal arrangement, up to about four process chambers can be mounted on a loadlock chamber.
A typical robot blade 10 is shown in FIG. 1. The robot blade 10 is constructed of a robot arm 12, and a wafer holder 14. The wafer holder 14 has a small thickness X such that it can go through narrow slit valves for delivering or withdrawing wafers to and from a process chamber or a cassette indexer. The robot arm 12 is constructed of a robot 18 and a mechanical arm 20. The wafer holder 14 is constructed of a blade portion 22, a pair of object sensors 24, 26 mounted in a top surface of the blade and a printed circuit board 32 for controlling the sensors 24, 26.
FIG. 1A shows a cross-sectional view of the wafer holder 14 holding a wafer 40 on top. In the configuration shown in FIG. 1A, a wafer 40 is carried on a top surface 16 of the blade 22. The object sensors 24, 26 are utilized to sense the presence of the wafer 40 which is properly positioned on the blade 22.
In utilizing the robot blade 10 shown in FIGS. 1 and 1A, the blade is used in a robot transfer system for transferring wafers between a load/unload chamber and a process chamber, for instance, during a pick/place actuation from chamber electrode/cassette. A serious processing problem arises in utilizing the robot blade, i.e., the scratching of wafer surfaces by the backside of the blade during a transfer in or out of a wafer cassette. Moreover, when a transfer has been made to a process chamber, the backside of the robot blade may scratch the top surface of a wafer pedestal and causing serious damages. In the normal configuration of a commercial robot blade, there is no provision for detecting any possible scratching or colliding of the blade with either a wafer or with a wafer pedestal. This presents a serious problem in that wafer scratching is frequently not detected such that problem persists until a large number of wafers have been scratched resulting in a great loss in throughput.
It is therefore an object of the present invention to provide an apparatus for transferring wafers by using a robot blade that does not have the drawbacks or shortcomings of the conventional robot blades.
It is another object of the present invention to provide an apparatus for transferring wafers by a robot blade that does not present the danger of scratching wafers in a wafer cassette.
It is a further object of the present invention to provide an apparatus for transferring wafers by a robot blade that does not present the danger of scratching a wafer pedestal in a process chamber.
It is another further object of the present invention to provide an apparatus for transferring wafers by a robot blade that is equipped with a distance sensor mounted in a bottom surface of the blade.
It is still another object of the present invention to provide an apparatus for transferring wafers by a robot blade that is equipped with a distance sensor mounted in such a way that a top surface of the sensor is flush with the bottom surface of the blade.
It is yet another object of the present invention to provide an apparatus for transferring wafers by a robot blade that is equipped with a capacitance sensor mounted in a bottom surface of the blade.
It is still another further object of the present invention to provide a method for transferring wafers by a robot blade by mounting a distance sensor in a bottom surface of the blade such that a minimum distance with an adjacent surface below can be maintained.
It is yet another further object of the present invention to provide a method for transferring wafers by providing a robot blade that is equipped with a capacitance sensor in a bottom surface of the blade, measuring a distance between the blade and an adjacent surface below, and stopping the blade motion when the distance measured is less than a minimum distance.